Tungsten and titanium films are frequently used in the manufacture of semiconductor devices, for example as diffusion barriers between silicon substrates and aluminum alloy metallizations. The titanium-tungsten (TiW) films are formed by sputtering titanium-tungsten targets.
During the sputtering process, titanium-tungsten material is sputtered from the surface of the target and deposited onto a substrate disposed opposite the surface of the target. However, the inventors have observed that nodules may form on the sputtering face of the target as material from the central portion of the target is sputtered and redeposited on the outer peripheral edge of the target face rather than on the substrate. Furthermore, the nodules have a tendency to flake and generate particles that can contaminate and adversely affect the quality of the deposited titanium-tungsten film on the substrate.
Accordingly, the inventors have provided improved methods and apparatus for controlling titanium-tungsten (TiW) target nodule formation.